Rat seminal-vesicle secretory protein SVS II binds DNA with a preference for the 5 ' regulatory region of secretory protein SVS IV gene: Co-isolationwith components of the nuclear matrix

In rats, the ventral prostate and seminal vesicles produce distinct sets of proteins whose functions and tissue-specific regulation by androgens remai n unclear. We have utilized the genes encoding the major secretory protein of seminal vesicles, SVS IV, and the C3 subunit of prostatein of the ventra l prostate to study how the nuclear matrix might determine their tissue-spe cific gene expression. Nuclear matrix proteins were prepared from purified nuclei with DNase and 2 M Nacl, separated in SDS gels, and transferred onto membranes for DNA-binding (southwestern) and immunological (western) analy ses. The 5' region of the SVS IV gene (SVS IV-7S) bound to a 45,000-kDa mol ecular-weight protein band in the nuclear matrix of seminal vesicles but no t to that of ventral prostate, kidney, or liver. Sequencing revealed that t his band was a seminal-vesicle secretory protein, SVS II, whose identity wa s confirmed with an anti-SVS II antiserum in western blots. Actin-like prot ein, similar in mobility to SVS II, was detected in seminal-vesicle and ven tral prostate nuclear matrix, but not in seminal-vesicle fluid. Reducing ag ent (10 mM dithiothreitol) and acidic (pH 6.5) buffer did not eliminate SVS II, but isolation of nuclear matrices with ammonium sulfate, nucleases, an d urea decreased SVS II immunoreactivity and removed actin-like protein. SV S II binding to SVS IV-7S DNA was greater than its binding to either a comp arable fragment of the C3 gene or linearized pUC-19 plasmid, and it was not eliminated by a 100-fold competition. When seminal-vesicle fluid was mixed with rat liver, some SVS II co-isolated with the nuclear-matrix proteins, indicating that nonspecific interactions contribute to its association with the nucleoskeleton, However, these interactions may not represent the intr acellular behavior of SVS II in seminal-vesicle epithelium. Sequence compar isons indicate significant homologies between SVS II and some other seminal proteins, including bovine caltrin, which, under the name seminalplasmin, is known to possess antimicrobial activity. Collectively, these data sugges t that in addition to its known functions, SVS II may also bind extraneous DNA in seminal fluid. Additionally, SVS II may participate as a structural component in the organization of a tissue-specific seminal-vesicle nuclear matrix.